<!--
Copyright (c) 2014 The Polymer Project Authors. All rights reserved.
This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
Code distributed by Google as part of the polymer project is also
subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
-->
<!--
@group Polymer Core Elements

The `<core-selection>` element is used to manage selection state. It has no
visual appearance and is typically used in conjunction with another element.
For example, [core-selector](#core-selector)
use a `<core-selection>` to manage selection.

To mark an item as selected, call the `select(item)` method on 
`<core-selection>`. The item itself is an argument to this method.

The `<core-selection>`element manages selection state for any given set of
items. When an item is selected, the `core-select` event is fired.

The attribute `multi` indicates if multiple items can be selected at once.
  
Example:
 
    <polymer-element name="selection-example">
       <template>
         <style>
           polyfill-next-selector { content: ':host > .selected'; }
           ::content > .selected {
             font-weight: bold;
             font-style: italic;
           }
         </style>
         <ul on-tap="{{itemTapAction}}">
           <content></content>
         </ul>
         <core-selection id="selection" multi
                         on-core-select="{{selectAction}}"></core-selection>
       </template>
       <script>
         Polymer('selection-example', {
           itemTapAction: function(e, detail, sender) {
             this.$.selection.select(e.target);
           },
           selectAction: function(e, detail, sender) {
             detail.item.classList.toggle('selected', detail.isSelected);
           }
         });
       </script>
    </polymer-element>

    <selection-example>
      <li>Red</li>
      <li>Green</li>
      <li>Blue</li>
    </selection-example>
 
@element core-selection
-->

<!--
Fired when an item's selection state is changed. This event is fired both
when an item is selected or deselected. The `isSelected` detail property
contains the selection state.

@event core-select
@param {Object} detail
  @param {boolean} detail.isSelected true for selection and false for de-selection
  @param {Object} detail.item the item element
-->
<link rel="import" href="../polymer/polymer.html">

<polymer-element name="core-selection" attributes="multi" hidden>
  <script>
    Polymer('core-selection', {
      /**
       * If true, multiple selections are allowed.
       *
       * @attribute multi
       * @type boolean
       * @default false
       */
      multi: false,
      ready: function() {
        this.clear();
      },
      clear: function() {
        this.selection = [];
      },
      /**
       * Retrieves the selected item(s).
       * @method getSelection
       * @returns Returns the selected item(s). If the multi property is true,
       * getSelection will return an array, otherwise it will return 
       * the selected item or undefined if there is no selection.
      */
      getSelection: function() {
        return this.multi ? this.selection : this.selection[0];
      },
      /**
       * Indicates if a given item is selected.
       * @method isSelected
       * @param {any} item The item whose selection state should be checked.
       * @returns Returns true if `item` is selected.
      */
      isSelected: function(item) {
        return this.selection.indexOf(item) >= 0;
      },
      setItemSelected: function(item, isSelected) {
        if (item !== undefined && item !== null) {
          if (isSelected) {
            this.selection.push(item);
          } else {
            var i = this.selection.indexOf(item);
            if (i >= 0) {
              this.selection.splice(i, 1);
            }
          }
          this.fire("core-select", {isSelected: isSelected, item: item});
        }
      },
      /**
       * Set the selection state for a given `item`. If the multi property
       * is true, then the selected state of `item` will be toggled; otherwise
       * the `item` will be selected.
       * @method select
       * @param {any} item: The item to select.
      */
      select: function(item) {
        if (this.multi) {
          this.toggle(item);
        } else if (this.getSelection() !== item) {
          this.setItemSelected(this.getSelection(), false);
          this.setItemSelected(item, true);
        }
      },
      /**
       * Toggles the selection state for `item`.
       * @method toggle
       * @param {any} item: The item to toggle.
      */
      toggle: function(item) {
        this.setItemSelected(item, !this.isSelected(item));
      }
    });
  </script>
</polymer-element>
